ABSTRACT
Electrophysiological experiments have been carried out on rats to examine the relationship between plasma extravasation into skin and antidromic activation of individual unmyelinated afferent fibres supplying cutaneous receptors, particularly polymodal nociceptors. Normal animals and ones in which the skin had been reinnervated after peripheral nerve transection 26-52 weeks before were studied. In the normal animals 12 of 18 (66%) polymodal nociceptor afferents showed evidence of plasma extravasation after antidromic stimulation of the nerve filament from which they were initially recorded. Antidromic stimulation of other types of unmyelinated unit gave no detectable signs of plasma extravasation. The results from the animals with regenerated nerves were similar with 15 of 21 (71%) of the polymodal nociceptor afferents showing clear signs of plasma extravasation after antidromic activation and the other types of unit giving no signs of such a response. These results show that while antidromic stimulation of a cutaneous nerve after intravascular administration of Evans Blue dye can be used to get a general view of the extent of innervation by polymodal nociceptors, it does not necessarily show the entire distribution of these receptors. It is likely that the ability or lack of ability of a polymodal nociceptor afferent to enhance vascular permeability, and so bring about plasma extravasation, is related to its neuropeptide content, and thus it follows that this might be a useful criterion for separating this broad class of cutaneous receptor into sub-groups.
Subject(s)
Neurons, Afferent/drug effects , Plasma/physiology , Skin Physiological Phenomena , Animals , Electrophysiology , Evans Blue , Male , Myelin Sheath/physiology , Nerve Regeneration , Nociceptors/drug effects , Nociceptors/physiology , Physical Stimulation , Rats , Rats, Inbred Strains , Skin/innervationABSTRACT
Electrophysiological experiment have been carried out on rats to see if the age at which a peripheral nerve injury occurs influences the success of regeneration. The assessment was made on the basis of two measures of peripheral nerve regeneration; the extent to which axons manage to grow across the injury site and into the distal stump, and their ability to resupply cutaneous structures with functional endings. Regeneration after nerve transection of both myelinated and unmyelinated axons was studied. The results showed that, apart from rats injured when 2 weeks old, the age at which injury occurred, over the range 4-40 weeks, had little bearing on the overall success of skin reinnervation. The 2-week-old rats showed significantly poorer recovery.
Subject(s)
Nerve Regeneration , Peripheral Nerves/physiology , Adrenergic Fibers/physiology , Afferent Pathways/physiopathology , Age Factors , Animals , Axons/ultrastructure , Electric Stimulation , Hindlimb/innervation , Male , Myelin Sheath , Peripheral Nerve Injuries , Peripheral Nerves/growth & development , Rats , Rats, Inbred Strains , Skin/innervation , Sweating/physiology , Tibial Nerve/growth & development , Tibial Nerve/injuries , Tibial Nerve/physiologyABSTRACT
Electrophysiological experiments have been carried out to investigate the time course and extent of sweat gland reinnervation in the rat hind paw. The first evidence of functional reinnervation after nerve transection was obtained at 12 weeks, when the extent of innervation was 20% of that measured in control animals. By 20 weeks, reinnervation had reached almost 50% of control values but then there was no further improvement up to 52 weeks. These results are comparable to those for skin reinnervation by polymodal nociceptor afferents.
